The present invention relates to an apparatus for slitting a traveling web of corrugated paperboard or the like and, in particular, to an idler roller assembly for supporting the running web below and in cooperation with an upper rotary slitting blade.
Apparatus for longitudinally slitting a continuous running web of corrugated paperboard is well known in the art. Such apparatus often includes a related mechanism for simultaneously providing longitudinal score lines in the advancing web, which score lines facilitate subsequent folding in the construction of boxes or the like. Thus, a combined slitter-scorer utilizes pairs of rotatable cutting tools and scoring tools disposed in the path of the advancing web of corrugated paperboard, with one tool of each pair disposed on an opposite side of the web. Typically, multiple slitting tools are mounted coaxially and laterally spaced across the width of the web and, likewise, multiple scoring tools are also coaxially mounted and spaced across the width of the web.
A conventional prior art device is shown for example in U.S. Pat. No. 4,627,214.
Each pair of upper and lower slitting tools is disposed with overlapping radial cutting edges between which the advancing paperboard web is moved to provide a continuous slit. Although commonly referred to as a "slitting" operation, the cutting tools of this type of prior art device in fact shear the moving sheet, resulting in a relative vertical displacement of the adjacent cut edges. However, problems arise as the thickness of the web increases, resulting in cuts which tend to become more ragged, edges which tend to be crushed, and a general degradation in the slit quality. Prior art methods also generate significant amounts of dust, resulting in a wide variety of well known environmental, operational, maintenance and quality control problems.
U.S. Pat. No. 5,090,281 discloses a slitting apparatus which represents a significant improvement in the above described prior art shear-type slitting apparatus. In this apparatus, the paperboard web is cut with a true slitting technique utilizing an apparatus in which the advancing web is directed through a thin circular blade rotating at high speed and running in the same direction as the web, with the board supported below the blade by rollers in contact with the underside of the web. This apparatus reduces significantly the generation of paperboard dust in the slitting operation and improves slit quality. However, particularly when used to slit a paperboard web at the dry end of a corrugating operation, there is a tendency for the adhesive used to bind the multilayer corrugated paperboard web to adhere to the cutting edge and side faces of the slitting blade. Typical paperboard adhesives are starch-based and the build up of adhesive on the blade carries with it some paperboard dust which is inevitably generated even in the improved slitting apparatus. The improved system described in the above identified patent also utilizes blade lubrication to prevent adhesive build up on the cutting blade. It has been found, however, that a corresponding build up of adhesive and paperboard dust occurs on the supporting rollers and, furthermore, the adhesive, dust particles, and the small pieces of board scrap generated during slitting tend to clog the slot in the supporting rollers in which the slitting blade is received.